Generally polyesters are produced by the reaction of di or polyols with a dicarboxylic acid such as terephthalic acid. These high molecular weight esters have found application in a number of areas including fibers and bottles. Polyesters are sensitive to moisture on processing. Care must be taken to reduce moisture levels in the resins to acceptable limits generally in the order of 0.02 percent or less. This is a particularly acute problem in compounding and molding polyesters such as polyethylene terephthalate (PET). Generally, in processing thermoplastics it is desirable to incorporate small amounts of nucleating agents in the composition to increase the rate of nucleation and crystalization, which reduces the time the thermoplastic is in the mold and the mold temperature required. The present invention seeks to meet these requirements by providing nucleating systems comprising organic anhydrides which may be used per se or in combination with other effective nucleating agents.
U.S. Pat. No. 4,558,096 issued Dec. 10, 1985 assigned to the Goodyear Tire and Rubber Company discloses a composition comprising 10 to 90 percent of polyethylene terephthalate from 10 to 90 percent of an ethylene propylene diene monomer (EPDM) rubber or an ethylene propylene rubber (EPR) and as a compatibilizer from 0.001 to about 2.0 weight percent of a C.sub.8-30 alkyl derivative of succinic anhydride and dimers and polymers of a specified formula containing a succinic anhydride residue in its backhome. The patent does not disclose or suggest that anhydrides per se are useful in a nucleating system.
U.S. Pat. No. 4,299,927 issued Nov. 10, 1981 to Eastman Kodak Company discloses a blend comprising 50 to 90 weight percent of a polyester, 50 to 10 weight percent of an anhydride modified polyolefin and 0.1 to 10 weight percent of a C.sub.4-22 alkyl derivative of succinic anhydride. The patent does not teach or suggest that anhydrides are useful in nucleating systems.
U.S. Pat. No. 4,351,758 issued Sept. 28, 1982 to Lu. et al discloses a high molecular weight terephthalate ester composition which has a moisture content of between 0.05 and 0.68 weight percent. The nucleating agents are alkali metal salts having anions which are oxides of elements of Group IV of the periodic table; talc and barium sulfate. The patent does not suggest that organic anhydrides could be used per se or in conjunction with other nucleating agents as a nucleating system.
There have been extensive studies of the heterogeneous nucleation of polyolefins and particularly polypropylene. These studies have generally concluded that the optimum nucleating agents for polypropylene are alkali metal salts of organic acids such as sodium benzoate or aluminum dibenzoate. Additionally it has been concluded that there should be a structural compatibility between the nucleating agents and the polymer. (Beck, H. N. (1967) Heterogeneous Nucleating Agents for Polypropylene Crystalization, J. Appl. Polym Sci 11, 673; Beck H. N. and Ledbetter H. D. (1965) DTA Study of Heterogeneous Nucleation of Crystallization in Polypropylene, J. Appl. Polym. Sci. 9,2131; Binsbergen F. L. (1970) Heterogeneous Nucleation in the Crystalization of Polyolefins: Part I Chemical and Physical Nature of Nucleating Agents, Polymer 11, 253; and Binsbergen F. L. (1973) Heterogeneous Nucleation in the Crystalization of Polyolefins III. Theory and Mechanism, J. Polym. Sci. Polym. Phys. Ed. 11, 117).
This art teaches away from using nucleating systems based on anhydrides. Generally, one skilled in the art would not have considered organic anhydrides as a basis for nucleating systems.
The present invention seeks to provide improved nucleating systems and polyester compositions which incorporate such nucleating systems.